They will pick one for you if you don't, most likely the cheapest less beneficial one. I don't feel like either plan matters just because they pretty much cover the basics and the extra are lame and irrelevant, just my opinion and in my county! Look into them though just to be sure.
No just call the office and ask which medicaid plans they accept and call them up anf sign uo with them.
Also.. I suggest that you shop around for those plans.. some of yhem have real neat benefits like physical therapy and stuff covered which will help u with your back pains if you choose to go to one. :)
Goodluck